Microfossils, a Key to Unravel Cold-Water Carbonate Mound Evolution through Time

34 Pages·2015·3.24 MB·English

RESEARCHARTICLE
Microfossils, a Key to Unravel Cold-Water
Carbonate Mound Evolution through Time:
Evidence from the Eastern Alboran Sea
ClaudioStalder1*,AgostinaVertino2,AntoniettaRosso3,AndresRüggeberg1,
ClaudiusPirkenseer1,JorgeE.Spangenberg4,SilviaSpezzaferri1,OsvaldoCamozzi1,
SachaRappo1,IrkaHajdas5
1 DepartmentofGeosciences,UniversityofFribourg,Fribourg,Switzerland,2 DepartmentofEarthand
EnvironmentalSciences,UniversityofMilano-Bicocca,Milano,Italy,3 DepartmentofBiological,Geological
andEnvironmentalSciences,UniversityofCatania,Catania,Italy,4 InstituteofEarthSurfaceDynamics,
UniversityofLausanne,Lausanne,Switzerland,5 IonBeamPhysics,EidgenössischeTechnische
HochschuleETHZürich,Zürich,Switzerland
*[email protected]
Abstract
OPENACCESS
Cold-watercoral(CWC)ecosystemsoccurworldwideandplayamajorroleintheocean's
Citation:StalderC,VertinoA,RossoA,Rüggeberg
carbonatebudgetandatmosphericCO balancesincetheDanian(~65m.y.ago).However
2
A,PirkenseerC,SpangenbergJE,etal.(2015)
theirtemporalandspatialevolutionagainstclimaticandoceanographicvariabilityisstill
Microfossils,aKeytoUnravelCold-WaterCarbonate
MoundEvolutionthroughTime:Evidencefromthe unclear.Forthefirsttime,wecombinethemainmacrofaunalcomponentsofasedimentcore
EasternAlboranSea.PLoSONE10(10):e0140223. fromaCWCmoundoftheMelillaMoundsFieldintheEasternAlboranSeawiththeassoci-
doi:10.1371/journal.pone.0140223
atedmicrofaunaandwehighlighttheimportanceofforaminiferaandostracodsasindicators
Editor:SigalAbramovich,BenGurionUniversityof ofCWCmoundevolutioninthepaleorecord.Abundancesofmacrofaunaalongthecore
theNegev,ISRAEL
revealalternatingperiodsdominatedbydistinctCWCtaxa(mostlyLopheliapertusa,Madre-
Received:June8,2015 poraoculata)thatcorrespondtomajorshiftsinforaminiferalandostracodassemblages.The
Accepted:September23,2015 perioddominatedbyM.oculatacoincideswithaperiodcharacterizedbyincreasedexportof
refractoryorganicmattertotheseafloorandratherunstableoceanographicconditionsatthe
Published:October8,2015
benthicboundarylayerwithperiodicallydecreasedwaterenergyandoxygenation,variable
Copyright:©2015Stalderetal.Thisisanopen
bottomwatertemperature/densityandincreasedsedimentflow.Themicrofaunalandgeo-
accessarticledistributedunderthetermsofthe
CreativeCommonsAttributionLicense,whichpermits chemicaldatastronglysuggestthatM.oculataandinparticularDendrophylliidaeshowa
unrestricteduse,distribution,andreproductioninany highertolerancetoenvironmentalchangesthanL.pertusa.Finally,weshowevidencefor
medium,providedtheoriginalauthorandsourceare
sustainedCWCgrowthduringtheAlleröd-Younger-DryasintheEasternAlboranSeaand
credited.
thatthisperiodcorrespondstostablebenthicconditionswithcold/denseandwelloxygenated
DataAvailabilityStatement:Allrelevantdataare
bottomwaters,highfluxesoflabileorganicmatterandrelativelystrongbottomcurrents
withinthepaperanditsSupportingInformationfiles.
Funding:ThisworkwasfundedbytheSwiss
NationalScienceFoundationwithgrants
200020_153125and200020_131829forCS(http:// Introduction
www.snf.ch/fr/Pages/default.aspx).Thefundershad
noroleinstudydesign,datacollectionandanalysis, Althoughcold-watercorals(CWCs)areknownsincecenturies,theybecameamajorresearch
decisiontopublish,orpreparationofthemanuscript. "hot"topiconlyinthelasttwodecades.Extensivestudies(e.g.,[1,2,3])havehelpedtoconstrain
theirgeographicaldistributionandtheiroccurrenceonthegeologicaltimescalebutstilllittleis
CompetingInterests:Theauthorshavedeclared
thatnocompetinginterestsexist. knownabouttheeffectsthatenvironmentalchangeshaveonCWCmounddevelopment.
PLOSONE|DOI:10.1371/journal.pone.0140223 October8,2015 1/34
Microfossils,aKeytoUnravelCold-WaterCarbonateMoundEvolution
Frame-buildingCWCspeciessettlemainlyonhardtopographichighs(e.g.,[1,3–6]),subverti-
calwallsandoverhangs[6–8]wherearelativelystronghydrographicregimepreventscorals
fromsedimentsmothering[9]andprovidethemwithfood(e.g.,[10,11]).Recently,aquarium
culturesoflivingCWCspeciescollectedfromtheNorthAtlanticandtheMediterraneanSea
andtheirδ13Candδ15NvaluesfromcoraltissueshaverevealedthatCWCsareabletofeedon
awiderangeoffoodsourcesincludingfreshmacrozooplankton,fecalpellets,degradedphyto-
detritus,dissolvedorganicmatterandbacteria(e.g.,[11–14]).
Comprehensivestudies(e.g.,[1,15,16])havedemonstratedthatthedistributionofCWCsis
largelydrivenbythechemo-physicalpropertiesofthesurroundingwatermasswhere,temper-
atures,salinitiesanddissolvedoxygencontentsusuallyrangewithin4–14°C,31.7–38.8and
2.6–7.2mll-1,respectively.Large-scalewatermassescharacterizationsinactiveCWCsettings
fromtheCelticandNorwegianshelvesanddistributedoverawidebathymetricrange(140–
850mwaterdepth)haveshownthatlivingcoralsthrivewithinawaterdensitygradientof
sigma-theta(σθ)=27.35to27.65kgm-3[17].IntheMediterraneanSea,livingCWCcolonies
havebeenfoundinwaterdensitiesof(σθ)=29.07to29.13kgm-3[7].
TheinterpretationofCWCpaleorecordsisusuallydifficultbecauseofthelargefluctuations
inthesedimentationratesandthefrequenthiatusescausedbystrongbottomcurrents(e.g.,
[18,19]).Furthermore,inmostcasesCWCsedimentsconsistentirelyofbiogenicfragmentsof
differentsizeandpreservationthatcomplicatesthepaleo-environmentalinterpretationofthe
sedimentaryrecordandspecificattributiontoepisodesofCWCgrowth,totemporarygrowth
interruptionsortothedemiseoftheCWCreef/moundinthepast.Nevertheless,itisessential
tounderstandtheresponseoffossilCWCtoclimateandoceanographicchangestopredict
theirfutureandtoevaluatehowmuchtheirexistencewillinfluencethetotalcarbonatebudget
andtheatmosphericCO onEarth[20].
2
Duringthelasttwodecades,onlyfewstudiesonlive(stained)anddead(fossil)benthicfora-
miniferaandostracodsassociatedtoCWCecosystemshavebeenreportedfromtheNorwegian
shelf[21–25],thePorcupineSeabightandRockallTrough[26–30],theGulfofCadizandthe
AlboranSea[31,32],theIonianSea[33],theTuscanArchipelago[34]andNovaScotia[35].
Severalofthosestudies(e.g.,[24,27,29])allowedgainingfurthercomprehensiononthedistri-
butionofspecifictaxaaccordingtosedimentaryfaciesandmicrohabitatsalongCWCmounds
andreefs.FreiwaldandSchönfeld[22]showedevidenceforpredationofHyrrokinsarcophaga
onliveCWCpolypswhereasMargrethetal.[27]proposedtheepibenthicspeciesDiscanoma-
linacoronataasapotentialbioindicatorforlivingCWCreefs.
Comparedtostudiesonmicroorganisms(foraminiferaandostracods),onlyfewofnumer-
ousstudiesonlivemacro-andmeiofaunafromCWCsettingsfocusedonthefossildistribution
(e.g.,[36,33,37]).Boththeskeletonisedbenthicmicroandmacrofaunastudiesassociatedto
CWCshaveclearlyshownthatforaminifera,ostracodsandmacrofaunamayprovideapower-
fulpaleoproxytounderstandlateralvariabilityandevolutionofCWCdevelopmentthrough
time(e.g.,[25–27,33,36]).
Weintegratestudiesonrecentbenthicmacro-andmicrofaunafromaCWCmoundofthe
easternAlboranSeaandtheirabundanceduringthelast13ka,withspecialemphasisonscler-
actinians,bryozoans,foraminiferansandostracodstorelatetheirevolutionthroughtimeand
theirresponsetopaleoceanographymodifications.Forthefirsttimewehavecross-correlated
bioticandgeochemicalproxiestointerprettheevolutionofaCWCmound.
GeologicalandOceanographicSettings
TheAlboranSeainthewesternMediterraneanSeaisa~400kmlongand~200kmwidebasin
withwaterdepthsnotexceeding2000m(Fig1)thatexhibitsacomplexseafloormorphology
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Microfossils,aKeytoUnravelCold-WaterCarbonateMoundEvolution
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Microfossils,aKeytoUnravelCold-WaterCarbonateMoundEvolution
Fig1.A.Mapshowingthemajorstudyareasoflive(stained)anddead(fossil)benthicforaminiferaandostracodsassociatedtocold-watercoral
ecosystems:theNorwegianshelf[21–25],thePorcupineSeabightandRockallTrough[26–30],NovaScotia[35],theGulfofCadizandAlboran
Sea[31,32],theIonianSea[33]andtheTuscanArchipelago[34].B.BathymetricmapoftheAlboranSeashowingthesurface-watercirculation
withtheeastern(EAG)andwesternAlborangyres(WAG),theAlboranRidge(AR)andtheSouthAlboranBasin(SAB).Theredstarshowsthe
locationofcoreTTR17-401G(251mwaterdepth)andthegreenstarsthelocationandwaterdepthsofadjacentcoresdiscussedinthisstudy:1,KS8230
(795m);2,TTR12-293G(1840m);3,GeoB13731-1(362m);4,TTR17-MS419G(410m);5,TTR17-MS411G(370m);6,MD95-2043(1841m).Thedashed
areasindicatethelocationandwaterdepthofcold-watercoralsamplesfromtheAlboranSeadatedwith14CandU/Th(<20kaBP):A,MelillaMoundsField
[42];B,NWCabliersBank[43]andC,SEIberianMargin[44]
doi:10.1371/journal.pone.0140223.g001
withseveralsub-basins,ridgesandseamounts[38].OurstudyareaislocatedintheSouth
AlboranBasin(SAB),whichisaNW-SEtrendingtectonicallycontrolledbasinboundingthe
southernflankoftheAlboranRidge[39].ItsformationstartedinthelateCretaceousasacon-
sequenceofcrustalextensioninasettingofoverallconvergenceoftheAfricanandEurasian
plates[40].ThisNorth-SouthconvergencewasreactivatedinthelatestTortonian[41].After
post-Messiniantimes,activecompressionalstructuressuchastheAlboranRidge(Fig1)or
strike-slipfaultssuchastheNektorfaultwereproduced[39].
TheMelillaMoundsField(MMF)islocatedinthesoutheasternAlboranSea(westernMed-
iterraneanSea)southeasttotheCapeTresForcas(Fig1).Thesubmarinemorphologyofthe
MMFischaracterizedbycarbonatemounds(Fig1),whichcoverasurfaceof~100km2within
awaterdepthrangeof250–600m[45].SimilarlytothemoundsinthenorthAtlantic,the
moundsoftheMMFformelongatedanddomedbiogeniccarbonatebuildupswithadiameter
rangingfrom48mto476m,upto100mhighabovetheseafloor,displayingamaximum
lengthof3000mandmostlyburiedbya1–12mthickfine-grainedsedimentarycover[42,45].
RadiocarbondatingsuggeststhattheCWCsoftheMMFstartedtodevelopduringthelate
Pleistoceneonunconformitiesandlandslides[42].Basedonvideosurvey,onlyafewliving
CWCcoloniesstilloccurintheMMFnowadays[46].
Fromanoceanographicpointofview,theAlboranSeabasinisapeculiarbasinstrongly
influencedbywaterexchangebetweentheAtlanticOceanandtheMediterraneanSea.Three
mainwatermassescharacterizethemodernwatermassconfigurationintheAlboranSea.The
upper~150–200mofthewatercolumnareoccupiedbyModifiedAtlanticWater(MAW)
(salinity=~36.2g/kg,T=~15°C)flowingfromtheAtlanticOceanthroughtheStraitof
GibraltartowardstheAlgerianBasin[47,48].TheMAWistransformedintheeasternMediter-
raneanSeabetweenRhodesandCyprusintotheLevantineIntermediateWater(LIW)[47,49].
Itoccursinwaterdepthsof200–600m,withasalinityof~38.4g/kgandameantemperature
of~13.3°C[47].TheWesternMediterraneanDeep-Water(WMDW;salinity=~38.4g/kg,T=
~12.8°C),formedintheGulfofLions(SEFrance)flowsbelowtheLIWinthedeepestpartof
theAlboranBasin[47,50].TheWMDWflowstowardstheAtlanticOceanandistopographi-
callyforcedtoshoalat~300mwaterdepthwhenpassingthesillofGibraltar[51].TheMedi-
terraneanOutflowWater(MOW),whichflowsintotheAtlanticOceanalongtheIberian
margin,iscomposedofLIWandWMDW[52].
IntheAlboranSea,theinflowingMAWformstwoanticyclonicgyresof~100kmindiame-
ter:theWesternAlboranGyre(WAG)andtheEasternAlboranGyre(EAG)(Fig1)[53].The
twogyresareroughlysituatedoverthewesternandeasternAlboranbasinswithrespective
maximumdepthsof1200and1800m.BothareseparatedfromeachotherbytheAlboran
Ridge[54].TheWAGandEAGdonothaveverystablepositionsorbehavioursgiventhe
strongseasonalvariationsinthesurfacecirculationoftheSAB[55].Insummer,bothgyresare
ratherconstant,butduringwintertheWAGoftenmigrateseastwardsandtheEAGevendisap-
pearsduetohigherMAWinflowandMOWoutflow.Furthermore,strongerwesterlywinds
[56]developajetalongtheAfricancoastinsteadofthegyre[54].
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Microfossils,aKeytoUnravelCold-WaterCarbonateMoundEvolution
ThemodernAlboranSeaisgenerallyoligotrophicwiththeexceptionoftwoareasofhigh
primaryproductivity[57].ThefirstareaissituatedonthenorthernlimboftheWAG,where
westerlywindscausetheupwellingofnutrient-richsubsurfacewatersandleadtoproduction
ratesofupto200gCm-2yr-1[58,59].Thesecondelevatedprimaryproductivitycentreis
locatedalongtheAlmeria-OranFrontandistriggeredbythedensitycontrastbetweenMAW
andresidentMediterraneansurfacewaterwithincreasedsalinity[57,60].
MaterialandMethods
The560cmlongsedimentcore401GwasrecoveredintheMelillaMoundsField(MMF)ata
waterdepthof251m(35°19.273'N,02°34.001'W)(Fig1)duringtheTraining-Through-
ResearchTTR17cruisein2008[61].Itconsistsofalternatinglayersofclayeytosandymud
bearingCWCfragmentsupto10cmlongandotherbenthicmacrofaunalcomponents.The
gravitycorewassampledeach20cmforgeochemicalandmicropaleontologicalinvestigations.
Sampleswereprocessedfollowingstandardproceduresforforaminiferalpreparation(see
[62,63]).Approximately10gofdrybulksedimentpersamplewaswashedthroughthreemesh
sieves(63,125and250μm)andatleast200specimensperfractionwerecountedandgluedon
plummer-cellsforarchive.Iftheresiduecontainedmorethanthetargetnumberof300benthic
foraminiferainasinglefraction,itsvolumewassplitwithadrysplitter.Iftheresiduecontained
lessthan300specimens,allspecimenswerecounted.Wedecidedtofocusonspecimenslarger
than125μm(S1Table)toexcludesmallerforms,whichareoftendisplacedbyredeposition
[64],andtomakethedatacomparabletootherbenthicforaminiferalstudiesinadjacentareas
(e.g.,[65–68]).Theplanktonicforaminiferaandostracodswereidentifiedonthe
fraction>250μmfollowingsimilarprocedures(S2andS3Tables).Theplanktonictobenthic
(P/B)ratiohasbeencalculatedbasedonthe>250μmsizefractiontoavoidoverestimationof
theratioduetotheredepositionofsmallerspecimens.
QuantitativeanalysesofbenthicforaminiferawereperformedwiththeSoftwarePRIMER6
[69].Thedatasetwasdouble-squareroottransformedtolimitthecontributionofmostabun-
dantandubiquitousspecies[70]andtheBray-Curtis(dis)SimilarityTermAnalysiswascalcu-
lated[71].ThesamesimilaritymatrixusedforBray-Curtis(dis)similaritieswasusedalsoto
obtainthenon-metricMultiDimensionalScaling(nMDS)plot[72].
Allrecognizableentirespecimensandskeletalfragmentslargerthan1mmwerecounted
andidentifiedtothelowestpossibletaxonomiclevel(familytospecies,withexceptionofAster-
ozoaandDecapodaidentifiedatsubphylumandorderlevel,respectively)(S4–S6Tables).
Moreover,duetothesmallsizeofimportantbryozoanspeciesbelongingtoCandidaeandCri-
sia,observationsonpresence/absenceofbryozoantaxawereperformedalsoonthe0.5–1mm
sedimentgrainfraction.
InordertooutlinethemainresultsofthemacrofaunaanalysisinFig2therelativeabun-
danceofthetwodominanttaxonomicgroups(Scleractinia,Bryozoa)collectedinthesediment
fraction1–10mmarepresented.Twomainsubgroups(“erectrigidCheilostome”and“erect
rigidTubuliporina”,Fig2,S5Table)wereselectedamongbryozoans.Theyincludethemost
representativespeciesintermsofabundanceandabundancevariationalongthecore.
RadiocarbondatingwasperformedattheEidgenössischeTechnischeHochschule(ETH)
Zürichusingtheacceleratormassspectrometry(AMS)technique.Fromselectedsamples,ben-
thicforaminiferawerepickeduntilatleast5–10mgofpurecarbonatewereobtained.Thespe-
ciesDiscanomalinacoronatalivesattachedtoahardsubstrateandisassociatedtotheCWC
ecosystem[27]andwaschosenwhereverpossible.Alternatively,theepibenthicforaminifera
Cibicideslobatuluswaspicked.Specimenswerecleanedinultrasoundstoremoveeventualcon-
tamination.Coralfragments(25–50mg)usedforradiocarbondatingwereselectedaccording
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Microfossils,aKeytoUnravelCold-WaterCarbonateMoundEvolution
Fig2.Distributionofmainmacrofaunalcomponents,benthicforaminifera,benthicforaminiferaassemblages(BFA)andostracodsincoreTTR17-
401G.ThechronologyofthecoreisbasedonAMS14Cagesofforaminiferaandcoralsandtheplanktonicforaminiferalturnover(PFT),expressedasa
maximumage.Therelativeabundanceofcoralsandbryozoansisexpressedaspercentageofthetotalnumberofcountedmacrofaunaspecimensper
sample.Therelativeabundanceofallmacrofaunalspecimenspersample(blackdottedline)isexpressedaspercentageofthetotalnumberofcounted
specimensinthecore.Therelativetaxonomicrichnesspersample(reddottedline)isexpressedaspercentageofthetotalnumberofmacrofaunataxafound
inthecoreanddoesnotincludescleractiniantaxa.Benthicforaminiferalspeciesrichness(SR)isexpressedasthetotalnumberofspeciesfoundineach
sample.Thedashedlinesdisplaychangesinthebenthicforaminiferalassemblages.
doi:10.1371/journal.pone.0140223.g002
totheirpreservationandfurthertreatedbystandardchemicalleachingprocedures.Table1
summarizesthescleractinianspeciesusedfortheAMS14Cdating.Theyweredissolvedincon-
centratedphosphoricacid[73]andtheextractedcarbondioxidewasconvertedintographite
asdescribedby[74].Allagesarecorrectedfor13Cand,assumingareservoiragecorrectionof
400years,the14Cageswereconvertedtocalendaryears(cal.yrBP;P=AD1950)usingthe
Marine13calibrationcurve[75]andsoftwareOxCalV4.2.4[76].Allagesarereportedaskilo-
yearsbeforepresent(kaBP;Table1).
ThestableisotopeanalyseswereperformedattheStableIsotopesLaboratoryoftheUniver-
sityofLausanne.Carbonandoxygenstableisotopecompositionofbenthic(Cibicideslobatu-
lus)andplanktonic(Globigerinabulloides)foraminifera(Table2)weredeterminedwiththe
ThermoFisherScientificcarbonatepreparationdeviceandGasBenchIIconnectedtoaDelta
PlusXLisotoperatiomassspectrometer(IRMS).Between5and15specimensofeachspecies
werepickedinthe>250μmandcleanedtwiceinanultrasonicbath.Thestablecarbonand
oxygenisotopicratiosarereportedindelta(δ)notationaspermil(‰)deviationrelativeto
ViennaPeeDeeBelemnite(VPDB)standard.Thestandardizationoftheδ13Candδ18Ovalues
relativetotheVPDBscalewasdonebycalibrationofthereferencegasandworkingstandards
withIAEAstandards.Analyticaluncertainty(1σ),monitoredbyreplicateanalysesofthe
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Microfossils,aKeytoUnravelCold-WaterCarbonateMoundEvolution
Table1. Radiocarbon14Cagesofsediment(benthicforaminifera)andcold-watercorals. Allagesarecorrectedforareservoirageof400years.
Core Coredepth Material SampleID] 14C-age 1σerror 2σrangecal.age Medianprobabilityage
(cm) (years) (±years) (yearsBP,P=AD1950) (yearsBP)
TTR17–401G 0 Fo–Lobatula ETH-55620 1055 28 552–671 611
TTR17–401G 0 CWC–Mo ETH-55621 5073 30 5316–5536 5426
TTR17–401G 80 CWC–Mo ETH-57100 5466 28 5746–5912 5829
TTR17–401G 200 CWC–Mo ETH-57101 10302 35 11168–11483 11326
TTR17–401G 240 CWC–Mo ETH-57102 10476 35 11362–11862 11612
TTR17–401G 260 Fo–Coronata ETH-55622 11146 56 12558–12763 12660
TTR17–401G 260 CWC–Lo ETH-55623 10770 39 12036–12448 12242
TTR17–401G 420 Fo–Coronata ETH-55624 11432 57 12731–13076 12903
TTR17–401G 420 CWC–Lo ETH-55625 11231 39 12610–12824 12717
TTR17–401G 560 Fo–Lobatula ETH-55626 11675 65 12987–13316 13151
TTR17–401G 560 CWC–Lo ETH-55627 11553 40 12880–13166 13023
Fo=Foraminifera;CWC=Cold-watercorals,Mo=Madreporaoculata,Lo=Lopheliapertusa
doi:10.1371/journal.pone.0140223.t001
internationalcalcitestandardNBS-19andthelaboratorystandardsCarraraMarblewasnot
greaterthan±0.05‰forδ13Cand±0.1‰forδ18O.Stablecarbonisotopecompositionofthe
organiccarbon(δ13C )wasdeterminedbyflashcombustiononaCarloErba1108elemental
org
analyzer(EA)connectedtoaThermoFisherScientificDeltaVIRMSthatwasoperatedinthe
continuousheliumflowmodeviaaConfloIIIsplitinterface(Table2).Thereproducibilityof
theEA-IRMSmeasurementisbetterthan±0.1%.Theaccuracyofanalyseswasassessedusing
internationalreferencestandards.
Totalorganiccarbon(TOC)content(inweight%)wasdeterminedatthelaboratoryofSedi-
mentGeochemistryattheUniversityofLausanneonabout100mgbulksedimentusingthe
Rock-Eval6technologyandfollowingthestandardrockpyrolysis[77,78].TheHydrogenIndex
(HI),expressedinmgHC/gTOC,displaysthetotalamountofpyrolyzedhydrocarbonsresult-
ingfromthecrackingofnon-volatileorganicmatter(HI=S x100/TOC)andtheOxygen
2
Index(OI,inmgCO /gTOC)whichaccountsfortheamountofCO generatedduringthe
2 2
pyrolysisofthekerogen(OI=S x100/TOC),bothnormalizedtoTOC.Additionalparameter
3
providedbytheRock-Eval6istheMineralCarbon(MINC),whichrepresentsthepercentage
ofcarbonderivedfrominorganicsources.AllRock-EvaldataaregiveninTable2.
Results
Chronology
Thechronologyofthecoresisconstraintby7AMS14CdatingonCWCfragmentsand4on
benthicforaminiferacoupledtothedistributionofplanktonicforaminifera(Fig2,Table1).
DiscrepanciesbetweencoralandbenthicforaminiferaagesareacommonfeatureinCWC
mounds(e.g.,[19,26,42]).Coralagesindicatethetimeswhentheorganismslivedwhileages
frombenthicforaminiferarepresentthesedimentationhistoryoftheCWCmound.However,
bothcanbeusedforpaleoceanographiccomparisonsbutinterpretationsshouldberelatedto
theorganism.TheradiocarbondatingrevealsthatcoreTTR17-401Gcoversthetimespan0.6–
13.1kaBP,thusreachingbacktothetransitionfromtheAllerödinterstadialtotheYounger-
Dryas(YD)coldevent(12.9–11.5kaBP).Thecalculatedlinearsedimentationrates(LSR)indi-
catethatthesedimentationwasshiftingbetweenextremevaluesof611cm/kafromthebaseto
260cm,and20.55cm/kafrom260cmtothetopofthecore.
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Table2. GeochemicaldataofcoreTTR17-401G. Areshowntotalorganiccarbon(TOC),mineralcarbon(MINC),hydrogenindex(HI),oxygenindex(OI),
planktonic(Globigerinabulloides)andbenthic(Cibicideslobatulus)δ18Oandδ13C,δ13C andgrain-sizedistribution.
org
Rock-Evalpyrolysis Stableisotopes(‰VPDB) Grain-size(%)
Depth TOC MINC HI OI δ13C δ13C δ18O δ13C δ18O >250μm 250– 125– <63μm
org lobatula lobatula bulloides bulloides
(cm) [% [%wt.] [mg [mg 125μm 63μm
wt.] HC/g CO /g
2
TOC] TOC]
0 0.7 5.76 99 278 -22.2 0.1 1.3 -0.8 0.6 58.29 1.11 0.68 39.91
20 1.07 3.71 102 212 -21.8 0.9 1.4 -1.1 0.8 15.61 0.33 0.92 83.14
40 0.98 3.8 84 211 -22.2 0.4 0.9 -0.5 0.8 14.05 0.83 1.83 83.3
60 0.86 5.34 90 224 -21.7 0.4 1.1 -1.2 0.6 50.58 0.41 1.49 47.52
80 1.03 3.74 95 224 -21.7 0.9 1.1 -0.6 0.9 14.55 0.61 2.42 82.41
100 1.14 3.95 90 191 -21.4 0.2 1.1 -0.5 0.9 31.77 0.87 0.77 66.59
120 1.05 3.73 98 221 -21.6 0.9 1.6 -0.7 1 14.52 0.98 1.09 83.41
140 0.93 4.52 92 213 -22 1 1.6 -0.5 0.9 45.58 0.92 0.5 53
160 0.98 3.23 82 220 -21.9 0.1 1.6 -1.1 0.7 1.28 0.46 0.74 97.52
180 0.97 3.43 86 219 -21.9 0.6 1.5 -1.1 0.6 41.42 0.79 1.8 55.99
200 0.87 5.11 78 202 -21.9 0.3 1.2 -1.4 0.4 38.87 0.92 3.72 56.5
220 0.95 4.35 102 195 -21.3 0.4 2.5 1.3 1.5 5.92 1.43 2.89 89.76
240 0.98 4.26 119 180 -21.1 1.2 2.5 0.6 2.3 42.82 0.73 5.25 51.19
260 0.71 7.03 112 243 -20.7 0.9 2.5 0.1 2.5 67.92 0.92 3.36 27.8
280 0.87 5.97 110 183 -20.8 0.9 2.7 0 2.2 54.34 1.28 2.01 42.37
300 0.8 6.7 105 220 -21.1 0.9 2.7 0.3 2.5 53.58 1.07 2.39 42.96
320 1.11 4.79 131 168 -21.2 1.1 2.9 -0.6 2.3 25.25 1.04 3.47 70.24
340 0.82 5.5 136 225 -21.3 0.8 2.6 0.4 2.5 48.8 1.19 2.59 47.41
360 0.92 5.51 119 186 -21.1 1 2.7 -0.7 1.7 25.66 2.96 5.36 66.02
380 0.85 4.83 124 187 -20.8 0.8 2.7 -0.5 2.6 12.53 2.93 10.03 74.51
400 0.99 4.71 112 179 -21.2 1 2.9 0.1 2.4 6.96 2.87 8.48 81.69
420 0.58 6.3 96 239 -21 0.8 2.6 -0.6 1.3 23.69 5.78 12.13 58.4
440 0.88 4.43 111 178 -21.4 0.9 2.8 -0.7 2.2 8.85 0.82 3.68 86.65
460 0.99 4.3 115 182 -21 1 2.7 0.5 2.6 15.49 1.18 2.65 80.67
480 0.96 4.09 119 177 -21 1.1 2.7 0.2 2.6 6.59 1.39 2.85 89.18
500 1.06 4.28 132 171 -21.2 0.7 2.8 -0.8 2.4 8.51 0.5 2.36 88.63
520 1 4.24 159 186 -21.2 0.2 2.6 -1 2.3 1.8 0.68 2.48 95.04
540 0.94 4.69 127 164 -21.5 -0.3 2.5 -1.1 1.8 2.7 0.84 2.95 93.51
560 0.68 5.79 117 199 -21 0.7 2.4 -1.1 1.9 4.97 1.31 5.5 88.23
doi:10.1371/journal.pone.0140223.t002
ThedatedCWCfragmentsyieldagesrangingfrom5.4atthetopofthecoreto13kaatits
base(Fig2).Apparently,theCWCsstoppedgrowing5.4kaatthecoretop,whichhasasedi-
mentageof0.6ka.Thisindicatesthepresenceofahiatusclosetothecoretopwithpossible
erosionofsediments.Becauseoftheagedifferencesbetweencoralsandsediments,thesedi-
mentrecordofcoreTTR17-401Gwillthereforebeexpressedinallfiguresversuscoredepth
andnotversusage.
Thedistributionofplanktonicforaminiferainthecoreshowstheoccurrenceoftwomajor
intervals,thefirstlastingfrom560to200cmanddominatedbyNeogloboquadrinaincompta
andthesecondfrom200cmtothetopanddominatedbyGloborotaliainflata(Figs2and3).
Thisplanktonicforaminiferalturnover(PFT)hasbeenwelldescribedintheAlboranSeaby
Rohlingetal.[79]andassumedtohaveoccurredaround8kaBP.Aroundthiscoredepth
PLOSONE|DOI:10.1371/journal.pone.0140223 October8,2015 8/34
Microfossils,aKeytoUnravelCold-WaterCarbonateMoundEvolution
Fig3.Multi-proxyrecordfromcoreTTR17-401G.Aredisplayedthelithologywithmainmacrofaunalcomponents,radiocarbonagesofsediment
(foraminifera),grain-sizedistribution(<63μm),totalorganiccarbon(TOC),δ13C ,δ13Candδ18Oofbenthicandplanktonicforaminifera.Benthic
org
foraminiferalassemblages(BFA)areshownaccordingtotheleveloftheBray-CurtiesSimilarity:BFAniandBFAgi(39%)andBFA1-BFA4(54%).Dashed
lineindicatestheturnoverintheplanktonicforaminiferalassemblage(PFA)atca.8kaBP[79].Freshwaterpulses1–4correspondtopossiblefreshening
eventsofthe(sub-)surfacewaters.
doi:10.1371/journal.pone.0140223.g003
anotherhiatusoccurredasindicatedbythedifferentagesbetweensediment(8ka)andcorals
(~11ka)(Fig2).
Stablecarbonandoxygenisotopesinforaminifera
Theplanktonicδ18Ovaluesdecreasetowardsthetopofthecoreandrangebetween0.4and
2.6‰(Fig3,Table2).IntheN.incomptadominatedinterval,theplanktonicδ18Ovalues(1.3–
2.6‰)arehigherthanduringtheG.inflatainterval(0.4–1‰).IntheintervaldominatedbyN.
incompta,theplanktonicδ18Ovaluesvarybetween2.2and2.6‰,exceptforsamples540–560,
420,360and220cmshowingrelativelylargenegativeexcursionsof1.9,1.8,1.3,1.7and1.5‰
respectively(Fig3,Table2).
Thebenthicδ18Ocurveshowsasimilarpatternastheplanktonicδ18Ocurvewithhigher
valuesof2.4–2.9‰intheintervaldominatedbyN.incomptacomparedtolowervaluesinthe
G.inflatainterval(0.9–1.6‰)(Fig3,Table2).Highestvaluesof2.9‰arereachedduringthe
earlyYD(12.6–12.9kaBP).IntheG.inflataintervalbenthicδ18Ovaluesshowadecreasein
twosteps,onefrom120–200cm(1.2–1.6‰)andanotheronefrom40–100cm(0.9–1.1‰)fol-
lowedbyanincreaseinthelast20cm(1.3–1.4‰)(Fig3).Therelativelylargenegativeexcur-
sionsobservedintheplanktonicδ18Ovaluescoincidewithdecreasesinthebenthicδ18O,from
PLOSONE|DOI:10.1371/journal.pone.0140223 October8,2015 9/34
Microfossils,aKeytoUnravelCold-WaterCarbonateMoundEvolution
whichthemostprominentoccursatthetransitionfromtheintervaldominatedbyN.incompta
toG.inflatawithadecreaseof-1.1‰intheplanktonicand-1.3‰inthebenthicδ18O.
Theplanktonicandbenthicδ13Cdisplayvaluesrangingfrom-1.4to1.3‰and-0.3to1.2‰
respectivelyandshowroughlyasimilarevolutionthroughoutthecore.Thehighestplanktonic
δ13Cvaluewasmeasuredintheinterval220–480cmwherethevaluesaregenerallyofamagni-
tudehigherthanfortheloweranduppersamples(Fig3).At200cm,theplanktonicδ13C
decreaseof-2.7‰coincideswiththetransitionfromtheN.incomptatotheG.inflatainterval
(Fig3).Similarly,higherbenthicδ13Cweremeasuredfrom480cmto240cm,wherevalues
dropfrom1.2to0.4‰,thusslightlybeforetheplanktonicδ13C(Fig3).Theinterval240–480
cmischaracterizedbyextremelystablebenthicδ13Csignalcomparedtomeasuredinthelower
andupperpartsofthecore.
Sedimentcharacterization:Rock-Evalpyrolysisandstablecarbon
isotopesofTOC
TheTotalOrganicCarbonshowsvaluesrangingfrom0.58–1.14%(Fig3,Table2).TOCvalues
tendtodecreasefromthebaseto260cmwiththreemarkedminimaat560,420and260cm
(Fig3).TOCvaluesincreasefrom240cmtoamaximumof1.14%at100cmbeforedecreasing
againintheuppermostpartofthecore(Fig3).TheTOCcontentdisplaysapositivecorrelation
tothemudfraction(Fig3).
TheMineralCarboncontentishigher(4.71–7.03%)intheinterval260–420cmcompared
totheintervals440–560cm(4.09–5.79%)and0–240cm(3.23–5.76%).TheMINCshowsarel-
ativelystrongnegativecorrelationtotheP/Bratio(Fig4).
TheHydrogenandOxygenIndexvaryfrom78–158mgHC/gTOCand164–278mgCO /g
2
TOCrespectively(Fig5;Table2).ArelativelycleartrendcanberecognizedwithhigherHI
andlowerOIintheintervaldominatedbyN.incomptaandlowerHIandhigherOIinthe
intervaldominatedbyG.inflata(Fig5;Table2).Thevaluesofδ13C rangefrom-22.2‰(0
org
cm)to-20.7‰(260cm).Theδ13C followsasimilartrendastheHIwithhighervalues
org
(-21.5–-20.7‰)intheN.incomptaintervalandlowervalues(-22.2–-21.4‰)intheG.inflata
interval(Fig3,Table2).Highestδ13C valuesaremeasuredwithininterval260–420cm(Fig
org
3).Theδ13C signalfollowswelltheplanktonicδ18Oandδ13Csignalwithmarkedminimaat
org
540,440,340and200cm.
Micropaleontology
CoreTTR17-401Gischaracterizedbyaconspicuousdistributionofthelarge(>250μm)
planktonicandbenthicforaminifera(S1andS2Tables).Thetargetvalueof200benthicspeci-
mensperfractioncouldbereachedonlyinthesamplesfrom260–420cmwheremostofthe
samplesweresplit.Inallothersamples,allspecimensoftheresiduewerecountedandamini-
mumwasobtainedat500cm(8specimens)andamaximumat540cm(110specimens).The
planktonicforaminiferashowedanoppositetrendwithlowestscores(71–202specimens)
between220and520cmandthetargetvaluereachedonlyat380cm(S2Table).Theplank-
tonicforaminiferacontributiontothetotalforaminiferafaunaiswelldocumentedintheP/B
ratio(Fig4).
Benthicforaminifera–univariatedistribution
Intotal,138benthicforaminiferaspecies(unstained)belongingto84generahavebeenidenti-
fiedincoreTTR17-401G(S1Table).Speciesrichness(SR)variesfrom34at500cmto61at
220cm.ThemostcommonspeciesfoundinthiscoreareBuliminaaculeata,Buliminamargin-
ata,Cassidulinalaevigata,C.lobatulus,Cibicidesrefulgens,Cibicidesungerianus(groupedas
PLOSONE|DOI:10.1371/journal.pone.0140223 October8,2015 10/34